1. (Field of the Invention)
This invention relates to a process for forming a MIS (metal-insulator-semiconductor) type structure electrode.
2. (Related Background Art)
It is essential for MIS type structure electrodes that the interface states density between the semiconductors and the insulation layer is low. For the improvement of their characteristics, Japanese Patent Laid-Open Publication Nos. 31170/1987 and 94944/1987 were proposed. GaAs semiconductors generally have interface states densities in the order of 10.sup.13 cm.sup.-2 eV.sup.-1 because of the difficulty of reconstructing dangling bonds on the interfaces. This is higher by about three orders, compared with the interface states density between silicon and silicon dioxide of MOS-FETs.
But recently it has been noted that ammonia sulfide (NH.sub.4).sub.2 S.sub.x containing excessive sulfur is used in sulfur passivation. Specifically, in Jia-Fa FAN, et.al., "Marked Reduction the Surface/Interface States of GaAs by (NH.sub.4).sub.2 S.sub.x Treatment" (Japanese Journal of Applied Physics, Vol. 28, No. 12 (December 1989), pp. L2255-L2257) it is confirmed that the interface states density on GaAs/SiO.sub.2 is reduced to 1.2.times.10.sup.11 cm.sup.-2 eV.sup.-1.
MIS FETs having good characteristics such as the interface states density which is higher by one order, compared with that of Si-system MOS FETs, can not be produced even by the use of this treatment. The inventors have made studied and found that a process for forming a MIS electrode which has succeeded in greatly decreasing the interface states density.